The main objective of the proposed research is to elucidate the mechanisms of action of a variety of toxins and drugs on nerve membranes. These toxins and drugs have been chosen on the basis of their specific and unique actions on the nerve membranes. Special emphasis will be placed on the interactions of those neuroactive agents with nerve membrane ionic channels. A variety of sophisticated electrophysiological approaches and techniques such as voltage clamp and internal perfusion will be employed to measure parameters associated with excitation. The proposed study will be conducted along three major lines of approach: 1) Interactions of toxins and drugs with ionic channels as manifested by changes in kinetics, ionic selectivity and voltage dependence; 2) Gating current as modified by these agents; and 3) Chemical modifications of membrane and ionic channels by specific protein reagents as manifested by alterations of actions of these toxins and drugs. The neuroactive agents to be studied include grayanotoxins, veratridine, palytoxin, anthopleurin-A, tetrodotoxin, saxitoxin and its derivatives, and aminopyridine and its derivatives. The data obtained in these three projects will be integrated at a high level to interpret the mechanisms of action of neuroactive agents at the membrane and molecular level.